DAMASCUS — Airstrikes and shelling pounded Aleppo for a third straight day on Sunday, killing two young siblings and at least 24 others in Syria’s largest city and former commercial capital.

The northern city has been bitterly contested between insurgents and government forces since 2012. Opposition groups control the eastern part of the city but have come under intense strain as the government has choked off all routes to the area except a narrow and perilous passage to the northwest.

At least 10 people were killed by rebel shelling on government-held areas in the city, according to activists and Syria’s state news agency, SANA. Rockets struck schools and residential areas, SANA reported. The Britain-based Syrian Observatory for Human Rights said two siblings were among the dead.

Airstrikes on the opposition side of the city killed 16, including a mother and her daughter, the Observatory said.

A video posted on social media by the Syrian Civil Defense first responder group, which is known as the White Helmets and operates in opposition-held areas, suggests some of the strikes hit a market in the neighborhood of Sakhour, with footage showing overturned vegetable carts among the wreckage.

The opposition High Negotiations Committee, which suspended its formal participation in peace talks with the government in Geneva last week, called the strikes ‘‘an attack on the Geneva process that is the only possible pathway to peace.’’

The cease-fire is still technically in place, but is unraveling on the ground.

Associated Press